1. Field of the Invention
This invention relates to a method for increasing the permeability to fluids of subterranean formations containing siliceous materials, and more particularly concerns a method for acidizing such formations penetrated by a well, especially acidizing the formation in depth away from the well.
2. Description of the Art
Acidizing of wells is a well-known process for increasing or restoring the permeability of subterranean formations so as to facilitate the flow of formation fluids, such as oil, gas or a geothermal fluid, from the formation into the well and also to facilitate the injection of fluids through the well into the formation. Acidizing involves treating the formation with an acid, typically hydrochloric acid, in order to dissolve the formation itself and/or clogging deposits, such as carbonate scale, thereby opening pores and other flow channels and increasing the permeability of the formation. Hydrofluoric acid or a mixture of hydrofluoric and hydrochloric acids, commonly known as "mud acid," is typically employed to dissolve siliceous materials.
Numerous acidizing methods have been proposed to cope with varying well conditions and special formation problems. Uowever, in recent years the increased activity in drilling very deep oil and gas wells and geothermal wells has outpaced the development of suitable acidizing methods, primarily due to the high temperature of these formations.
One problem encountered during acidizing of all formations, especially high temperature formations, is that the acid is rapidly consumed by the reactive material immediately adjacent the borehole before the acid can penetrate any significant distance into the formation. Without adequate formation penetration, the acidizing operation is of limited value. To this end, various additives have been proposed for addition to acidizing compositions to retard the reaction of the acid with the formation or clogging deposits in the formation. Retarders are used in an effort to inject live acid farther out into the formation before the acid reacts completely, thus increasing the permeability of the formation farther from the wellbore.
In other well treatments as disclosed in our copending application Ser. No. 506,537, filed June 21, 1983, it is known to attempt to maintain the permeability of a formation containing loose finely divided particulate matter by injecting therein an organosilane or an ester of an organosilane. It is believed that the injected materials coat the formation fines, polymerize, bind the fines in place and reduce their tendency to shift position, lodge in pore restrictions and reduce formation permeability when fluids are subsequently passed through the formation.
While these and other treatments have met with some success in particular applications, the need exists for a further improved well treating process to increase the permeability of a subterranean siliceous formation, particularly in depth away from a well penetrating the formation.
Accordingly, a principal object of this invention is to provide a method for acidizing a subterranean siliceous formation.
It is a further object to provide such a method for acidizing those siliceous materials contained in portions of the formation which are relatively remote from a borehole.
It is a still further object to provide such a method for acidizing in depth all types of siliceous materials present in the formation.
It is another object to overcome the problems associated with rapid spending of the acidizing solution within a relatively short radial distance from the borehole.
It is yet another object to acidize in depth away from a borehole those formations having a relatively high temperature.
Other objects, advantages and features of this invention will become apparent to those skilled in the art from the following description and appended claims.